[flashrom] [PATCH RFC] Access PCI BARs through sysfs

[Ed Swierk]

Thanks for the feedback. I cleaned up the code so it should compile on
all the supported systems.

Only then did I discover a much simpler approach. It turns out that
Linux (recent versions, at least) allow selective mmap access to
/dev/mem even with various strict security features enabled. Simply
not calling iopl() solves the problem.

I've posted a new patch for review.

--Ed


On Sat, Feb 28, 2015 at 4:08 PM, Stefan Tauner
<stefan.tauner at alumni.tuwien.ac.at> wrote:
> On Thu, 26 Feb 2015 13:53:13 -0800
> Ed Swierk <eswierk at skyportsystems.com> wrote:
>
>> On Thu, Feb 26, 2015 at 4:10 AM, Patrick Georgi <pgeorgi at google.com> wrote:
>> > 2015-02-26 1:57 GMT+01:00 Ed Swierk <eswierk at skyportsystems.com>:
>> >> Running flashrom on a Linux system with CONFIG_STRICT_DEVMEM=y, I can now
>> >> successfully program the SPI flash on an Intel 10G NIC using the
>> >
>> >> +#if !defined(__DJGPP__) && !defined(__LIBPAYLOAD__)
>> >> +static void *pcidev_mapbar_sysfs(struct pci_dev *dev, const char *descr, int bar, off_t offset, size_t length)
>> > Isn't that actually Linux specific, instead of non-djgpp-or-libpayload specific?
>>
>> I suppose that's a safe assumption, though I don't know much about any
>> of the other platforms flashrom supports. libpci already figures out
>> whether the platform supports sysfs. I piggyback off that logic by
>> checking pacc->method.
>>
>> Here we're just deciding whether the platform uses mmap() to access
>> physical address space. I followed the same approach used in
>> physmap.c, since pcidev_mapbar_sysfs() is doing the same thing as
>> sys_physmap_rw_uncached(), just with a PCI resource file instead of
>> /dev/mem.
>>
>> But I can switch to #if IS_LINUX if you think that's clearer. We can
>> revisit that if and when some other sprouts a similar mmapped sysfs
>> interface to PCI resources.
>
> I have not really looked into the patch... but I did a little compile
> test on top of r1885. I'll just let the buildbot speak for itself:
> http://buildbot.flashrom.org/buildresults/flashrom-000164-Zcc/results.txt
> sparc7 is expected to fail with r1885.
>
> --
> Kind regards/Mit freundlichen Grüßen, Stefan Tauner